The long-term goal of the proposed research is to understand the[unreadable] mechanisms of regulation of mitochondrial biogenesis in Saccharomyces[unreadable] cerevisiae. First, we will elucidate the functions of a putative ATP-[unreadable] dependent RNA helicase in mitochondria encoded by the nuclear suv3 gene.[unreadable] Suv3 is involved in various post-transcriptional activities in[unreadable] mitochondria, and is essential for maintenance of the wild-type[unreadable] mitochondrial genome. The properties of a mutant allele of sur3, call[unreadable] SUV3-1, suggests that suv3 functions in group I intron splicing, and in[unreadable] particular, to resolve excised group I introns from ribonucleoprotein[unreadable] (RNP) splicing complexes. This model will be tested, including the[unreadable] notion that SUV3-1 is a compromised RNA helicase. These studies will be[unreadable] extended to characterize group I intron RNP complexes, with initial[unreadable] emphasis on an 18S ribonucleoprotein particle containing the excised[unreadable] omega intron of the 21S rRNA gene. Using strains with an intronless[unreadable] wild-type mitochondrial genome, we will initiate studies to determine[unreadable] other functions of suv3 in mitochondrial RNA metabolism. Our second[unreadable] objective is to characterize a novel regulatory path we discovered called[unreadable] retrograde regulation, whereby the functional state of mitochondria can[unreadable] profoundly affect nuclear gene expression. We have proposed, and provided[unreadable] evidence supporting the idea, that retrograde regulation is a mechanisms[unreadable] for the cell to adjust to changes in mitochondrial function, biogenesis[unreadable] and inheritance. We wish to elucidate the mechanisms of signaling from[unreadable] mitochondria to the nucleus. Here, we will focus on two novel genes,[unreadable] RTG1 that encodes a new member of the basic helix-loop-helix (bHLH)[unreadable] family of transcription factors, and RTG2 that encodes a protein of[unreadable] unknown function. The products of both genes are required for retrograde[unreadable] regulation of the CIT2 gene, which encodes a peroxisomal isoform of[unreadable] citrate synthase that functions as part of the glyoxylate cycle.[unreadable] Retrograde regulation of CIT2 functions metabolically to provide citrate[unreadable] to mitochondria from the glyoxylate cycle under conditions where the TCA[unreadable] cycle may be limiting. Our aims are to 1) determine how the bHLH[unreadable] protein, RTG1, acts as a transcriptional switch for retrograde[unreadable] regulation; 2) determine the function of RTG2; 3) define through genetics[unreadable] and molecular approaches additional components of the retrograde pathway;[unreadable] and 4) elucidate the blocks in metabolic communication between the TCA[unreadable] and glyoxylate cycles in rtg1 and rtg2 mutants. These experiments should[unreadable] provide additional insights into the function of retrograde regulation.[unreadable]